The invention relates to a pipe of oriented thermoplastic polymeric material and also to a method of manufacturing such a pipe.
In our UK Pat. No. 1 432 539 we have taught a method of, and apparatus for, forming a pipe from orientable thermoplastic polymeric material by radially expanding a tubular blank into a mould at a temperature at which expansion of the pipe will cause oriention of the polymer molecules. In this manner the finished pipe has an oriented structure capable of withstanding a greater hoop stress for a given wall thickness that a pipe made of the same material which has not been oriented, and has an enlarged oriented socket for carrying a sealing ring. In this manner a pipe was produced with an integral socket having a specified bursting strength with a smaller wall thickness than was previously possible, thereby reducing the volume of plastics used for a given pipe diameter and strength and minimising the cost of the materials required. Such pipes are typically manufactured from PVC, chlorinated PVC, high or low density polyethylene, polypropylene or ABS, although other suitable orientable polymers may be used. As the enlarged socket is of greater diameter than the remainder of the pipe, the wall of the socket is thinner than the pipe wall and consequently more flexible.
In practice we have found that, whilst the reduced rigidity of the socket is not critical, large diameter pipes subjected to high pressures can incur leaks past the socket seal due to the increased flexibility of the thinner socket wall.